Oil well cement fluid loss agent and preparation method thereof

Abstract

The invention belongs to the technical field of oil well cement fluid loss agents, and particularly relates to an oil well cement fluid loss agent and a preparation method thereof.The oil well cement fluid loss agent is prepared from, by weight, 20-30 parts of cellulose, 1-15 parts of urea, 50-200 parts of a sodium hydroxide aqueous solution, 25-50 parts of N, N-methylene bisacrylamide and 20-35 parts of binary unsaturated carboxylic acid; the fluid loss agent provided by the invention has the advantages of excellent fluid loss reduction capability, excellent high-temperature resistance and excellent high-temperature stability.

Description

Technical Field

[0001] This application belongs to the technical field of fluid loss additives for oil well cement, and particularly relates to a fluid loss additive for oil well cement and a preparation method thereof. Background Art

[0002] Fluid loss additives for cement can enhance the water retention of cement slurries during oil well cementing operations, prevent premature dehydration of cement slurries in permeable formations, ensure the stability of cement slurries, improve the strength of solidified cement stones, prevent gas channeling, improve the impermeability of cement rings, protect water-sensitive formations, prevent pollution of oil and gas layers by cement slurry filtrate, and prevent blockage of oil and gas layers by cement slurry particles.

[0003] Currently, two commonly used fluid loss additives in China, such as polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC), both have different defects. The PVA-based fluid loss additive has the advantages of low price and gas channeling prevention, has no retarding effect at low temperatures, and has good compatibility with calcium chloride, but has poor high-temperature adaptability, and the maximum use temperature can only reach 95°C, and its salt resistance (NaCl) is poor, and the salt resistance ability usually does not exceed 5%. Cellulose-based fluid loss additives such as HEC have a moderate price and strong fluid loss reduction performance, but have obvious thickening effects, and at the same time will delay the setting time of cement slurries, and because the ether bonds in the molecular cyclic chain units will undergo oxidative decomposition at high temperatures, the use temperature generally does not exceed 110°C.

[0004] In view of this, how to obtain a fluid loss additive with high salt resistance, a wide applicable temperature range, and high cement stability has become increasingly important. Summary of the Invention

[0005] This application provides a fluid loss additive for oil well cement and a preparation method thereof to solve the technical problems of poor salt resistance, narrow applicable temperature range, and low stability of cement slurries in existing technologies.

[0006] In a first aspect, this application provides a fluid loss additive for oil well cement, which includes: cellulose, urea, sodium hydroxide aqueous solution, N,N-methylenebisacrylamide, binary unsaturated carboxylic acid, and initiator.

[0007] In an optional embodiment, the binary unsaturated carboxylic acid is selected from any one of itaconic acid, maleic acid, or fumaric acid; The weight-average molecular weight of the fluid loss additive is 2×10 5 ~4×10 5 , for example, 2.1×10 5 , 2.2×10 5 , 2.3×10 5 , 2.4×10 5 , 2.5×10 5, 2.6×10 5 , 2.7×10 5 , 2.8×10 5 , 2.9×10 5 , 3.2×10 5 etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0008] In an alternative embodiment, based on parts by weight data, the fluid loss reducer comprises 20 - 30 parts of cellulose, 1 - 15 parts of urea, 50 - 200 parts of sodium hydroxide aqueous solution, 25 - 50 parts of N,N - methylenebisacrylamide, and 20 - 35 parts of binary unsaturated carboxylic acid.

[0009] In an alternative embodiment, the initiator is selected from potassium persulfate or ammonium persulfate; The addition amount of the initiator is 1% - 6% of the total mass of the fluid loss reducer.

[0010] In an alternative embodiment, the fluid loss reducer further comprises 1 - 5 parts of quaternary ammonium salt cationic monomer and / or quaternary ammonium salt anionic monomer.

[0011] In an alternative embodiment, the pH value of the sodium hydroxide aqueous solution is 4 - 6.

[0012] In a second aspect, the present application provides a preparation method of an oil well cement fluid loss reducer, and the preparation method includes: After mixing and stirring cellulose, urea, and sodium hydroxide aqueous solution, place it in an environment below zero degrees Celsius, take it out and place it in a room temperature environment for stirring to dissolve the cellulose; Add N,N - methylenebisacrylamide and binary unsaturated carboxylic acid to the above solution, and in a nitrogen environment, add an initiator and a quaternary ammonium salt cationic monomer and / or a quaternary ammonium salt anionic monomer; Place the mixed solution in an environment below zero degrees Celsius for 1 - 30 minutes, stir and react at a certain temperature for 0.5 - 1 hour, and then place it below zero degrees Celsius again, repeating this process multiple times to obtain a gel, and after drying, make it into a powder to obtain the fluid loss reducer.

[0013] In an alternative embodiment, the reaction temperature is 60 - 80 °C.

[0014] In an alternative embodiment, the total reaction time does not exceed 6 hours.

[0015] In a third aspect, the present application provides an oil well cement, and the oil well cement comprises the fluid loss reducer in any one of the embodiments of the first aspect of the present application, and / or the fluid loss reducer prepared in any one of the embodiments of the second aspect of the present application.

[0016] The present application provides a fluid loss reducer for oil well cement and a preparation method thereof. Compared with the prior art, the following beneficial effects are also achieved: 1. In the present application, the cellulose is first dissolved to ensure that the molecular weight of the fluid loss reducer can be controlled within a certain range, thereby better regulating the performance of the fluid loss reducer. After the cellulose is dissolved, it is mixed with N,N-methylenebisacrylamide and a binary unsaturated carboxylic acid, and then repeatedly switched between a certain low temperature and a high temperature. This not only ensures that the cross-linking reaction enables the fluid loss reducer to form a network structure, but also controls the growth of fiber crystals, enabling the fluid loss reducer to form a more complex network structure and enhancing the fluid loss reduction performance.

[0017] 2. Through the synergistic effect of cellulose, N,N-methylenebisacrylamide and a binary unsaturated carboxylic acid, it is possible to overcome the "inverted" phenomenon of the thickening time of the fluid loss reducer formed by amide and unsaturated carboxylic acid; ensure the thickening time of the fluid loss reducer, and at the same time, enable the fluid loss reducer to still have good stability and low water loss under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0019] Figure 1 Process flow diagram of a preparation method of a fluid loss reducer for oil well cement provided by the present application.

[0020] Through the above-mentioned drawings, specific embodiments of the present application have been shown, and more detailed descriptions will be given later. These drawings and text descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below in conjunction with the drawings in the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments in the present application belong to the scope of protection of the present application.

[0022] In the description, claims, and above-mentioned drawings of this application, terms such as "first", "second", "third", "fourth", etc. (if any) are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented, for example, in an order other than those illustrated or described herein.

[0023] In the embodiments of this application, words such as "exemplary" or "for example" are used to represent examples, illustrations, or explanations. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or having more advantages than other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0024] The following is to prepare a fluid loss reducer through Examples 1 to 3 and Comparative Examples 1 to 3. The fluid loss reducers in Examples 1 to 3 are prepared by the following method: S101. Mix and stir cellulose, urea, and an aqueous sodium hydroxide solution, then place it in an environment below zero degrees Celsius. After taking it out, place it in a room temperature environment and stir to dissolve the cellulose.

[0025] S102. Add N,N-methylenebisacrylamide and a binary unsaturated carboxylic acid to the above solution. In a nitrogen environment, add an initiator and a quaternary ammonium salt cationic monomer and / or a quaternary ammonium salt anionic monomer.

[0026] S103. Place the mixed solution in an environment below zero degrees Celsius for 1 to 30 minutes, stir and react at a certain temperature for 0.5 to 1 hour, and then place it back below zero degrees Celsius again. Repeat this process multiple times to obtain a gel. After drying, make it into a powder to obtain the fluid loss reducer.

[0027] Specifically, the preparation of the fluid loss reducer is described in detail through the following steps. Example

[0028] A method for preparing a fluid loss reducer, comprising: S201. Mix and stir cellulose, urea, and an aqueous sodium hydroxide solution, then place it in an environment of -10°C. After taking it out, place it in a room temperature environment and stir to dissolve the cellulose.

[0029] S202. Add N,N-methylenebisacrylamide and maleic acid to the solution in S201. In a nitrogen environment, add 5% initiator potassium persulfate and a quaternary ammonium salt cationic monomer and a quaternary ammonium salt anionic monomer.

[0030] S203. Place the mixture in an environment at -5°C for 30 min, stir and react at 60°C for 1 h, then place it back at -5°C, and repeat this process 3 to 5 times to obtain a gel. After drying, make it into a powder to obtain the fluid loss reducer.

[0031] Among them, 30 parts of the above-mentioned cellulose, 15 parts of urea, 150 parts of sodium hydroxide aqueous solution, 40 parts of N,N-methylenebisacrylamide, 30 parts of maleic acid, 5 parts of quaternary ammonium salt cationic monomer and quaternary ammonium salt anionic monomer. Example

[0032] The difference between this example and Example 1 is only that the components of the fluid loss reducer include 20 parts of cellulose, 12 parts of urea, 120 parts of sodium hydroxide aqueous solution, 30 parts of N,N-methylenebisacrylamide, 23 parts of itaconic acid, and 3 parts of quaternary ammonium salt cationic monomer and quaternary ammonium salt anionic monomer Example

[0033] The difference between this example and the example is only that the components of the fluid loss reducer do not include 5 parts of quaternary ammonium salt cationic monomer and quaternary ammonium salt anionic monomer.

[0034] Comparative Example 1 The difference between this comparative example and Example 1 is only that in step S203, the mixture is directly stirred and reacted at 60°C for 5 h to obtain a gel, which is dried and made into a powder to obtain the fluid loss reducer.

[0035] Comparative Example 2 The difference between this comparative example and Example 1 is only that the fluid loss reducer does not include cellulose and urea, and step S201 is not included in the preparation steps. In S203, the mixture is reacted at 60 - 80°C to obtain.

[0036] Comparative Example 3 The difference between this comparative example and Example 1 is only that the component of the fluid loss reducer does not contain urea, and the preparation steps do not include step S201.

[0037] Performance test: Calculate according to the mass of the cement used when preparing the cement slurry for the fluid loss reducers obtained in Examples 1 - 3 and Comparative Examples 1 - 3. According to the addition amount of the fluid loss reducer between 1 - 1.2 wt%, prepare the cement slurry according to the method specified in GB10238 oil well cement, with a density of 1.56 g / cm 3 , and evaluate the performance according to the relevant component composition and test method of the prepared cement slurry in accordance with GB / T19139 - 2012 and SY / T5504.2 - 2013.

[0038] Among them, the above-mentioned oil well cement used is ordinary G - grade oil well cement purchased on the market.

[0039] In addition, 0.5 wt% of a retarder (GWR-300L) and 0.2 wt% of an antifoaming agent (GWX-1L) were added to the cement slurries in each of the above-mentioned examples and comparative examples. The test results are shown in Table 1. Table 1. Test Results: Note: In the above table, " / " indicates that the cement paste is too thick and hardly flows, and it is not recommended to use; "piercing" indicates that the water loss cannot be effectively controlled and the cement filter cake cannot be formed. During the cementing operation, it is easy to cause bridge plugging and cementing accidents, so it is not recommended to use either.

[0040] As can be seen from Table 1, for the cement slurries prepared by adding the fluid loss additives in Examples 1 to 3, at 220 °C, the fluid loss can reach below 34 mL, and even when the application temperature is as high as 232 °C, the fluid loss can also be guaranteed to be below 37 mL, showing excellent fluid loss reduction ability, indicating that the fluid loss additive of the present application has excellent high-temperature resistance and high-temperature stability.

[0041] In Comparative Example 1, since the growth of fibrous crystals was not controlled under low-temperature conditions, cellulose, N,N-methylenebisacrylamide, and unsaturated carboxylic acid could not play a synergistic role, resulting in a serious decline in the performance of the fluid loss additive; similarly, the performance of the fluid loss additives in Comparative Examples 2 to 3 was also worse than that of the fluid loss additives in Examples 1 to 3.

[0042] So far, the technical solutions of the present application have been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An oil well cement fluid loss reducer, characterized in that, The fluid loss reducer includes: cellulose, urea, sodium hydroxide aqueous solution, N,N-methylenebisacrylamide, binary unsaturated carboxylic acid and initiator.

2. The fluid loss reducer for oil well cement according to claim 1, characterized in that, The binary unsaturated carboxylic acid is selected from any one of itaconic acid, maleic acid or fumaric acid; The weight average molecular weight of the fluid loss reducer is 2×10 5 ~4×10 5 .

3. The fluid loss reducer for oil well cement according to claim 1, characterized in that, Calculated by weight data, the fluid loss reducer includes 20-30 parts of cellulose, 1-15 parts of urea, 50-200 parts of sodium hydroxide aqueous solution, 25-50 parts of N,N-methylenebisacrylamide, and 20-35 parts of binary unsaturated carboxylic acid.

4. The fluid loss reducer for oil well cement according to claim 1 or 3, characterized in that The initiator is selected from potassium persulfate or ammonium persulfate; The addition amount of the initiator is 1%-6% of the total mass of the fluid loss reducer.

5. The fluid loss reducer for oil well cement according to claim 1 or 3, characterized in that, The fluid loss reducer also includes 1-5 parts of quaternary ammonium salt cationic monomer and / or quaternary ammonium salt anionic monomer.

6. The fluid loss reducer for oil well cement according to claim 1 or 3, characterized in that, The pH value of the sodium hydroxide aqueous solution is 4-6.

7. A preparation method of a fluid loss reducer for oil well cement, characterized in that, The preparation method includes: After mixing and stirring cellulose, urea and sodium hydroxide aqueous solution, place it in an environment below zero degrees Celsius, take it out and place it in a room temperature environment for stirring to dissolve the cellulose; Add N,N-methylenebisacrylamide and binary unsaturated carboxylic acid to the above solution, and add initiator and quaternary ammonium salt cationic monomer and / or quaternary ammonium salt anionic monomer under a nitrogen environment; Place the mixed solution in an environment below zero degrees Celsius for 1-30 minutes, stir and react at a certain temperature for 0.5-1 hour, and place it back below zero degrees Celsius again. Repeat this several times to obtain a gel, dry it, and make it into a powder to obtain the fluid loss reducer.

8. The preparation method of a fluid loss reducer for oil well cement according to claim 7, characterized in that, The reaction temperature is 60-80 °C.

9. The preparation method of a fluid loss reducer for oil well cement according to claim 7, characterized in that, The total reaction time does not exceed 6 hours.

10. An oil well cement, characterized in that, The oil well cement includes: the fluid loss reducer described in any one of claims 1-6, and / or the fluid loss reducer prepared by the preparation method described in any one of claims 7-9.

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